Apparatus and method of producing semiconductor rods by pulling the same from a melt



Jan. 3, 1967 w. KELLER 3,296,036

APPARATUS AND METHOD OF PRODUCING SEMICONDUCTOR RODS BY PULLING THE SAMEFROM A MELT Filed Oct. 22, 1965 2 Sheets-Sheet 1 Fig.1

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Jan. 3, 1967 W. LLER 3,296,036

ICON TOR ROD APPARATUS AND THOD OF P UCING SEM 5 BY U LING THE SAME FROMA MEL Filed Oct. 22, 1965 2 Sheets-Sheet 2 nit "sent 3,296,036 APPARATUSAND METHOD OF PRODUCING SEMICONDUCTOR RODS BY PULLIN G TIE SAME FROM AMELT Wolfgang Keller, Pretzfeld, Germany, assignor toSiemens-Schuckertwerke Aktiengesellschaft, Berlin- Siemensstadt,Germany, a corporation of Germany Filed Oct. 22, 1965, Ser. No. 502,054Claims priority, applicatiggfigrmany, Mar. 19, 1965, 19 Claims. (Cl.148--1.6)

This application is a continuation-in-part of my application Serial No.351,032, filed March 11, 1964, now abandoned.

My invention relates to apparatus and method for producing semiconductorrods by pulling the same from a melt of semiconductor material.

Monocrystalline semiconductor rods have been produced in the past bypulling them from a melt according to the Czochralski method and bycrucible-free zone melting according to the method of Theuerer. Morerecently, the so-called Podest process has become known (see the articleby Dash on page 363 of Growth and Perfection of Crystals, edited byDoremus, Roberts and Turnbull, pulished by John Wiley & Sons, Inc., NewYork, and Chapman and Hall, Ltd., London, 1958). A drop-shaped melt isproduced on a slotted or split semiconductor rod, for example by meansof induction heating, and a monocrystal is drawn out of this melt afterimmersing a monocrystalline seed therein.

In the method of pulling monocrystals from a melt in a crucible, thediameter of the growing semiconductor material is controlled byregulating the temperature of the melt and the speed at which thepulling takes place or both. By using a monocrystalline seed,semiconductor monocrystals of larger diameters can be produced in thismanner. This method, however, has a disadvantage in that impurities,such as oxygen, can diffuse into the melt from the heated crucible Wall.With materials that melt at high temperatures, such as silicon forexample, further difficulties arise due to the fact that the cruciblewall becomes plastically deformable at those high temperatures. With thecrucible-free zone melting method, monocrystals with a diameter of morethan 25 mm. can be produced only with great difficulty, and it is almostimpossible to produce monocrystals of more than 35 mm. diameter.

It is accordingly an object of my invention to provide an apparatus andmethod of producing semiconductor rods which avoids the disadvantages ofthe previously known apparatuses and methods and which permits theproduction of semiconductor rods of relatively large diameters withease.

It is another object of my invention to provide an apparatus and methodof producing semiconductor rods in which the semiconductor rods that aregrown are of relatively large diameter and are monocrystalline.

It is an additional object of my invention to provide an apparatus andmethod of producing semiconductor rods wherein contamination bydiffusion from the crucible walls is prevented by making the cruciblewalls proper of the same highly purified semiconductor material.

It is a concomitant object of my invention to provide an apparatus andmethod of producing semiconductor bodies wherein the body that is grownis practically undisturbed while it is being heated and the growingcrystal accordingly has exceptionally few dislocations, a feature whichis known to be particularly important in the production ofmonocrystalline semiconductor bodies that are to be used as electroniccomponents.

In accordance with an aspect of my invention, I provide an apparatus andmethod of producing semiconduc tor rods by pulling the same from a meltin which a rod component, i.e. a seed crystal particularly, is immersedin a melt and is enlarged as it is pulled out. A substantiallycylindrical semiconductor carrier element is provided, having alongitudinal axis extending in a vertical direction, and thesemiconductor carrier element is rotated continuously about this axis.The semiconductor body is heated from above by means of a heating devicedisposed at one side of the rotational axis and extending up to aboutthe center of the body cross section, and the rod portion beyond theheated portion of the melt is pulled out of the latter.

In accordance with another aspect of my invention and in order to avoidimperfections of the growing semiconductor monocrystal, it is pulledfrom the melt outside of the field of the induction heating coil in thecase where heating is carried out by induction.

In accordance with a further aspect of my invention, the semiconductorbody is heated from below by means of a heating device disposed at oneside of the rotational axis thereof and extending to the center of thebody cross section, and the rod portion beyond the heated portion of themelt is pulled out of the latter in a downward direction.

The novel features which are considered as characteris tic for theinvention are set forth in particular in the appended claims.

While the invention has been illustrated and described as apparatus andmethtod of producing semiconductor rods by drawing them from a melt, itis not intended to be limited to the details shown, since variousmodifications and structural changes may be made without departing inany way from the spirit of the present invention. Such adaptationsshould, and are intended to be comprehended within the meaning and rangeof equivalents of the claims herein.

The invention itself, however, both as to its construction and itsmethod of operation, together with addition al objects and advantagesthereof, will be best understood from the following description ofspecific embodiments when read in connection with the accompanyingdrawings, in which:

FIG. 1 is a diagrammatic cross section of, a vacuum chamber in which themethod of this invention can be carried out;

FIG. 2 is an enlarged perspective view of the central components shownin the vacuum chamber of FIG. 1;

FIGS. 3 and 4 are top plan views of modifications of the componentsshown in FIG. 2;

FIG. 5 is a perspective view of an additional modification of thecomponents shown in FIG. 2;

FIG. 6 is an enlarged partial front elevational view of a modificationof the components shown in FIG. 2; and

FIG. 7 is a partly sectional bottom plan view of FIG. 6 taken along thelines VIIVII in the direction of the arrows.

Referring now to the drawings and particularly to FIG. 1 thereof, thereis shown a vacuum chamber comprising a box-type housing 2 provided witha viewing glass or window 3 through which the method carried outinaccordance with my invention inside the chamber can be observed. Insteadof a vacuum, a protective gas can be supplied to the housing 2 in orderto carry out the method of this invention. The chamber can be evacuatedor supplied wtih protective gas through the connecting tube 4. A thickrod 5 as well as a slender rod 6, both consisting either of silicon orgermanium, are located inside the chamber, the slender rod 6 beingproduced or grown from and carried by the thick rod 5. A melt 7 islocated between the rods 5 and 6 and is formed by heating and meltingthe top of the rod 5 3 With an induction coil 8, but can also be formedsimilarly by radiation heating or electron radiation. The induction coil8 is secured to a support 9 of suitable insulating material which doesnot melt or vaporize at the employed temperatures. The support 9 extendsoutwardly from the chamber 2 through a vacuum-proof orprotective-gas-proof fitting 10, as the case may be, located in anopening at the bottom wall of the chamber 2. The support 9 has at leastone longitudinal bore through which the electrical leads to the heatingcoil 8 and a coolant supply and discharge means for cooling the heatingcoil extend. The two-headed arrow 11 indicates that the heating coil 8and the support 9 are displaceable from outside the vacuum chamber in avertical direction as viewed in FIG. 1.

The thick rod is supported by a lower holder 12 that is secured at anend of a guide rod 13 which is also led to the outside through avacuum-proof or protective-gas-proof fitting 14, as the case may be,also mounted in an opening provided in the base wall of the chamber. Theguide rod 13 can also be actuated from the outside for displacement inthe vertical direction as viewed in FIG. 1 as well as for turning aboutits axis as indicated by the pertinent two-headed and curved arrows. Theslender rod 6 is held in a similar manner as the thick rod 5 in an upperholder 15 which is secured at the end of a shaft 16. The shaft 16 alsopasses through a vacuumor protective-gas-proof fitting 17, as the casemay be, mounted in an opening in the top Wall of the chamber and is alsodisplaceable in a vertical direction from the outside as viewed in FIG.1, as well as rotatable about its own axis as shown by the relatedarrows.

In FIG. 2, portions of the thick rod and the slender rod are shown in anenlarged view as engaging one another in a melt. As is apparent from thedrawing, the slender rod portion 6 lies remote from the effects of theheating coil 8 and is therefore able to grow completely undisturbedthereby. The heating coil 8 produces a heating effect on the portion ofthe end surface of the thicker rod 5 which lies beneath it, causing itto melt. By continuous rotation of the thicker rod 5 about itslongitudinal axis, every portion of the outer end surface of the thickrod is subjected to the heating efiect of the coil 8. On the other hand,the slender rod 6 which is located eccentrically with respect to thelongitudinal axis of the thick rod 5 is not affected by the heatingdevice. It is understood, of course, that instead of the single Windingof the illustrated heating coil 8, a heating coil with several windings,such as two or three, for example, can be employed. The slender rod 6 isadvantageously rotated about its own axis so as to ensure symmetricalcrystalline growth thereof. The thick rod 5 is suitably a cylindricalsemiconductor body of silicon or germanium. Slight variations in thediameter of the cylindrical rod 5 are of no significance. Also slightvariations in the shape of the cylinder, for example where a slighttaper of the surface gives it a somewhat conical appearance, are notharmful for carrying out the method of this invention. Naturally, it isparticularly advantageous when the rod is substantially a geometricallyperfect cylinder.

In FIG. 3 there is illustrated a slightly modified heating coil 8a inwhich one of the leads is shown as being drawn off straight from theheating loop rather than having a bend as in the embodiment of FIG. 2.

In FIG. 4 there is shown another heating coil 8b which differs from thatof FIGS. 2 and 3. The induction heating coil 8b of FIG. 4 has the formof a segment of a circle. The point of the circular segment is locatedat the rotational axis of the cylindrical thick rod 5. Such a shape ofthe induction heating coil produces a fairly uniform depth penetrationof the applied heat overthe entire surface of the melt 7 as the rod 5 isrotated.

The entire upper surface of the thick rod 5 is advantageously not heatedbut rather, a predetermined margin located between the arc-shapedportion of the coil 8b and the edge of the rod 5 remains unheated, whichprevents dripping of the melt from the upper surface of the rod.

It is advisable to supply the melt continuously with new semiconductormaterial from an outside source and thereby prevent the cylindricalsemiconductor body 5 from being entirely consumed. In such a case thecylindrical semiconductor body 5 can be kept relatively short in lengthas shown in FIG. 5. The semiconductor material which is supplied to themelt is preferably in the form of another semiconductor rod and is alsopreferably introduced in the vicinity of the heater so that it will meltas soon as possible. In the case where heating is effected by aninduction-type heating coil as shown in FIG. 5, the additionalsemiconductor material in the form of the rod 18 is introduced into themelt through the circular turn of a heating coil 8c. The cylindricalsemiconductor body 5 in such a case is not necessarily but preferablysurrounded by a graphite crucible 19. In order to reduce the heatingcapacity or necessary heating power for the induction heating coil 80,the graphite crucible 19 is preheated; for example in the case wheresilicon is the semiconductor, the cylindrical semiconductor body andcrucible are preheated to about 1200 C. Other types of preheating canalso be provided, for example by means of an induction heating coilwhich surrounds the thick rod 5 in the vicinity of the melt 7.

It is of course also contemplated within the scope of my invention toapply heat to the top of the thick rod 5 on one side of the verticalaxis and to rotate the rod 5 to produce the melt 7 by other heatingmeans than the induction coil 8, 8a, 8b, 80. As aforementioned, suchapplications can be made by radiation heating, electron radiationheating, or the like.

In the embodiment of FIGS. 6 and 7, the lower end of a preferablycylindrical semiconductor body 22 is heated by a liquid cooled inductioncoil 24 which can have one or more windings and can also have otherforms such as a segment of a circle having an acute central angle orhaving a crescent shape as in FIG. 7. By employing lowfrequency heatingcurrent the magnetic supporting effect exerted by the coil on the meltcan be increased to such an extent in comparison to its heating effectthat engage ment of the heating coil 24 by the melt 25 is prevented.This can also be achieved by providing an additional coil beneath thesemiconductor body which is supplied with an alternating current of forexample 10 kilocycles. Due to the rotation of the semiconductor bodyabout its longitudinal axis, the heating output therefrom is distributeduniformally over the entire cross section so that the melt 25 spreadsout over the entire end surface of the semiconductor body. After dippinga seed crystal into the melt, the monocrystalline thin semiconductor rod23 is drawn therefrom, its growth being uninfluenced by the heatingaction. To obtain a symmetrical growth of the semiconductor rod 23 it isrotated about its longitudinal axis. The direction of the arrow 27indicates the direction in which the semiconductor rod 23 is beingpulled from the melt 25. The semiconductor body 22 can be preheated bythe coil 26 or in any other manner so that the required heat output ofthe coil 24 is reduced. The coils 24 and 26 are secured to a carrier(not shown) displaceable in a vertical direction as viewed in FIG. 6which can also contain the electrical leads as well as the coolant loopconduits. Since the semiconductor body 22 becomes shorter in lengthduring the pulling operation, the coils 24 and 26 are made to followafter it as it reduces in length in the direction shown by the arrow 28.Naturally, the coils 24 and 26 can also remain at rest and thesemiconductor body 22 can be guided in a downward direction as the lowerend of the rod is being diminished. Since the process is preferablycarried out in vacuum, the holders of the semiconductor body 22 and ofthe thin semiconductor rod 23 as well as the carrier for the coils 24and 26 must extend outwardly from the vacuum vessel through suitablyapertured, vacuum-tight inserts in the wall thereof similar to theinserts 10, 14, 17 of the embodiment shown in FIG. 1. The consumption ofthe cylindrical semiconductor body 22 can be reduced by continuallysupplying new semiconductor material preferably in rod form to the melt.The new semiconductor material is expediently supplied to the vicinityof the heating action, through the heating coil when induction heatingis employed, in order to achieve a rapid melting thereof. Thus in theembodiment of FIG. 7, in a manner similar to that of FIG. 5, except forthe fact that the melt is at the bottom end of the semiconductor bodyrather than at the top end thereof, a supply of semiconductor material,in the form of a rod 30 (FIG. 7), for example, can be continuously addedto the melt through the space within the coil 24.

I claim:

1. Method of producing a monocrystalline semiconductor body whichcomprises horizontally rotating a melt of semiconductor materialsimultaneously with a carrier of the same material underlying andsupporting the melt; applying heat at a radially extending areaoverlying the rotating melt so as to heat the melt as it passes beneaththe area to at least the melting temperature of the material; andpulling with the aid of a crystal seed a mono crystalline semiconductorbody from a portion of the melt distantly located from the appliedheating area.

2. Method of producing a monocrystalline semiconductor body whichcomprises horizontally rotating a melt of semiconductor materialsimultaneously with a carrier of the same material underlying andsupporting the melt; applying heat at a radially extending areaoverlying the rotating melt so as to heat the melt as it passes beneaththe area to at least the melting temperature of the material; pullingwith the aid of a crystal seed a monocrystalline semiconductor body froma portion of the melt distantly located from the applied heating area;and supplying additional semiconductor material in solid form to themelt to replenish the material pulled from the melt.

3. Method of producing a monocrystalline semiconductor rod whichcomprises horizontally rotating a substantially cylindrical block ofsemiconductor material simultaneously with a melt of the same materialcarried by the block; applying heat at a radially extending areaoverlying the rotating melt so as to heat the melt as it passes beneaththe area to at least the melting temperature of the material; andpulling with the aid of a crystal seed a monocrystalline semiconductorrod from a portion of the melt distantly located from the heating area.

4. Method of producing a monocrystalline semiconductor rod whichcomprises horizontally rotating a substantially cylindrical block ofsemiconductor material simultaneously with a melt consisting of the samematerial which is supported by the block; applying heat at a radiallyextending area overlying the rotating melt so as to heat the melt as itpasses beneath the area to at least the melting temperature of thematerial; pulling with the aid of a crystal seed a monocrystallinesemiconductor rod from a portion of the melt distantly located from saidheating area; and introducing semiconductor material in rod form to saidmelt from above the same to replace the material pulled from said melt.

5. Method of producing a monocrystalline semiconductor rod whichcomprises horizontally rotating a substantially cylindrical carrier ofsemiconductor material simultaneously with a melt consisting of the samematerial and supported on the carrier; applying heat at a radiallyextending area overlying the rotating melt so as to heat the melt as itpasses beneath the area to at least the melting temperature of thematerial; pulling with the aid of a crystal seed a monocrystallinesemiconductor rod from a portion of the melt distantly located from saidheating area; and introducing semiconductor material in solid form tothe melt through the heating area from above the melt so as to replacethe material pulled from the melt.

6. Method of producing a monocrystalline semiconductor rod whichcomprises horizontally rotating a substantially cylindrical carrier ofsemiconductor material simultaneously with a melt consisting of the samematerial overlying and supported by the carrier; applying heat at afixed area overlying the rotating melt and extending radially to amarginal area adjacent the periphery of the cylindrical carrier so as toheat all of the melt encircled by the marginal area as it passes beneaththe heating area to at least the melting temperature of the material;and pulling with the aid of a crystal seed a monocrystallinesemiconductor rod from a portion of the melt distantly located from saidheating area.

7. Apparatus for producing a monocrystalline semiconductor bodycomprising a semiconductor carrier, means for rotating saidsemiconductor carrier about a vertical axis, means for applying heatfrom a position above said carrier, onto an upper face of said carrierover a fixed area extending radially outwardly from the vicinity of saidvertical axis, said upper face of said carrier being rotatable throughsaid area to form a melt of semiconductor material around said verticalaxis; and means for pulling a crystal seed and consequent semiconductorgrowth thereon from said melt at a location distant from said heatingarea.

8. Apparatus according to claim 7 including means for supplyingsemiconductor material to said melt from above the same so as to replacethe material pulled therefrom.

9. Apparatus according to claim 8 wherein said heat applying meanscomprises an induction heating coil located above and spaced from saidmelt, said coil having the shape of a sector of a circle with its vertexdirected toward said vertical axis, the area defined by saidsectorshaped coil corresponding substantially to said heat-applyingarea.

10. Apparatus according to claim 9 including means for adjusting thespacing between said induction heating coil and said melt.

11. Method of producing a monocrystalline semiconductor body whichcomprises horizontally rotating a melt of semiconductor material andsupporting the melt on a carrier simultaneously rotating therewith,applying heat at a radially extending area adjacent the surface of therotating melt so as to heat the melt as it passes the applied heatingarea to at least the melting temperature of the material; and pullingwith the aid of a crystal seed a monocrystalline semiconductor body froma portion of the melt distantly located from the applied heating area.

12. Method according to claim 11, wherein the melt underlies thecarrier, the applied heating area underlies the melt so as to heat themelt from below and the monocrystalline semiconductor body is pulledfrom the melt in a downward direction.

13. Method according to claim 12 wherein the melt is supported by amagnetic field.

14. Method according to claim 12 including preheating the semiconductormaterial in the vicinity of the melt.

15. Apparatus for producing a monocrystalline semiconductor bodycomprising a semiconductor carrier, mean-s for rotating saidsemiconductor carrier about a vertical axis, means for applying heatfrom a position adjacent an axial end of said carrier onto an end faceof said carrier over a fixed area extending radially outwardly from thevicinity of said vertical axis, said end face of said carrier beingrotatable through said area to form a melt of semiconductor materialaround said vertical axis; and means for pulling a crystal seed andconsequent semiconductor growth thereon from said melt at a locationdistant from said heating area.

16. Apparatus according to claim 15 wherein the position of said heatapplying means is located below said carrier for applying heat onto alower face of said carrier.

17. Apparatus according to claim 16 including means 7 8 -for supplyingsemiconductor material to said melt from 1 for preheating saidsemiconductor carrier in the vicinity below the same so as to replacethe material pulled thereof said melt.

from.

18. Apparatus according to claim 16 wherein said heat 1 l d f 0d l t'app ylng means me u es means or pr uclng a magne 1c 5 DAVID L. RECKPrimary Examinerfield for supporting the melt.

19. Apparatusaccording to claim 15 including means N. F. MARKVA,Assistant Examiner.

No references cited.

1. METHOD OF PRODUCING A MONOCRYSTALLINE SEMICONDUCTOR BODY WHICHCOMPRISES HORIZONTALLY ROTATING A MELT OF SEMICONDUCTOR MATERIALSIMULTANEOUSLY WITH A CARRIER OF THE SAME MATERIAL UNDERLYING ANDSUPPORTING THE MELT; APPLYING HEAT AT A RADIALLY EXTENDING AREAOVERLYING THE ROTATING MELT SO AS TO HEAT THE MELT AS IT PASSES BENEATHTHE AREA TO AT LEAST THE MELTING TEMPERATURES OF THE MATERIAL; ANDPULLING WITH THE AID OF A CRYSTAL SEED A MONOCRYSTALLINE SEMICONDUCTORBODY FROM A PORTION OF THE MELT DISTANTLY LOCATED FROM THE APPLIEDHEATING AREA.